Not applicable.
Not applicable.
(1) Field of the Invention
The present invention generally relates to welding equipment and processes. More particularly, this invention relates to an arc-welding overlay apparatus having improved integration, reliability and ease of use, and capable of producing quality welds under harsh conditions.
(2) Description of the Related Art
Overlay welding generally involves depositing weld material over a surface region in a series of beads with some lateral overlapping, forming a continuous layer of weld material that increases the thickness and strength of the region. Overlay welds are often deposited by shielded metal-arc welding in the restoration of large vessels used in industries such as utilities, co-generation refining, petrochemical, pulp and paper, and waste-to-energy. A particular use of overlay welds is in the repair of boiler panels, though overlay welding is also useful in repairing individual boiler tubes, smaller pressure vessels, nozzles and pipe sections of a boiler. Overlay weld material can be deposited manually or with the use of an automatic or semiautomatic welding machine mounted in the vicinity of the region being welded.
Accuracy and consistency of all parameters are critical during an overlay welding process, which can be difficult to achieve if the overlay welding equipment must perform in a harsh environment. Welding defects that can occur include cold laps on weld overlay starts and stops, burn-throughs, and overlay deposited with improper shielding gas pressure (necessitating removal and re-application of the weld). There is also the difficulty of tying two sections of overlay together with minimal or no preparation work to the overlay sections being tied. A variety of machine overlay welding equipment has been developed, such as U.S. Pat. Nos. 4,019,016, 4,631,385, 5,070,792 and 5,220,145. These and other commercially-available machine overlay welding equipment may make use of variable speed travel carriages and modular drive systems. However, such equipment has not been found to meet the rigors of the environment in which weld repairs of boilers must be performed. Existing welding equipment also have a limited level of integration that cannot satisfy a variety of repair applications of the type associated with the restoration of boilers and their associated components.
In view of the above, it would be desirable if an improved overlay welding apparatus were available for performing weld repairs, particularly in demanding applications.
The present invention provides an overlay welding apparatus that is capable of increasing the accuracy and consistency of essentially all welding parameters, such that a more consistent overlay repair can be obtained even in a harsh repair environment. More particularly, the invention is an electric-arc welding overlay apparatus with improvements over the prior art that render the apparatus capable of greater mechanical weld head stability, and provides external oscillator stroke adjustment and electronic circuitry that control movement of the arc along the desired weld path. The overlay welding apparatus of this invention also provides for the control of the welding current, carriage speed, wire feed speed and oscillation speed so as to reduce the incidence of cold laps on weld overlay starts and stops, burn-throughs, and overlay deposited with improper shielding gas pressure.
The above features of the invention are provided with an arc welding overlay apparatus that comprises an electric power source for producing a welding current, a track on which a welding head carriage is adapted for movement, an index arm mounted for movement in a direction substantially transverse to the track, a slide mounted for movement in a direction substantially transverse to the index arm, a welding torch mounted to the slide by which the welding current maintains an electric arc with a workpiece, and means for dispensing a filler material to the welding torch. The welding apparatus is further equipped with means for providing feedback signals that sense the travel speed of the weld head carriage on the track, the transverse movement of the index arm, the length of the electric arc produced by the welding torch, and the rate at which filler material is dispensed by the dispensing means. Control means are provided to operate on the basis of these feedback signals to control the travel speed of the weld head carriage, the transverse movement of the index arm, the length of the electric arc, and the rate at which the filler material is dispensed.
The welding apparatus also preferably includes means for delivering a shielding gas to the welding torch, and means for sensing the delivery of the shielding gas by the delivering means so that adequate shielding gas flow is maintained. In addition, the welding apparatus preferably includes means for oscillating the welding torch relative to the index arm. Additional preferred aspects of the welding apparatus of this invention include a modular design for ease of maintenance, and the ability to step or ramp all control parameters up and down, adjust stick-out (electrode extension), and monitor and record control parameters at predetermined intervals for later inspection to evaluate weld quality. Another preferred aspect is the capability for automatic emergency shutdown during shielding gas or carriage speed failures.
The invention utilizes the above improvements and preferred aspects to provide a universal welding system that is highly integrated and reliable compared to overlay welding apparatuses of the prior art, yet is sufficiently uncomplicated to be used by operators with limited experience. In addition, the overlay welding apparatus can be employed in a wider variety of applications than prior art apparatuses, with the capability of producing quality welds under harsh conditions.
Other objects and advantages of this invention will be better appreciated from the following detailed description.